Synchronous motors, which include a primary part having coils and a secondary part having permanent magnets, have been known for a long time. For example, U.S. Pat. No. 5,642,013 describes synchronous motors in which magnets are placed in evenly spaced fashion and with alternating polarity on a magnetic path. Opposite this magnetic path is a primary part, on whose teeth coils are wound. In response to suitable energizing of the coils, a force is able to be generated between the primary part and the secondary part which drives the synchronous motor. The magnetic paths may be disposed on the lateral surface of a cylinder in order to form a rotary motor, or along a straight line in order to form a linear motor. The magnetic paths may also extend along curved paths, such as in a transport system, for example, to move movable carriages having an integrated primary part along any paths as desired.
The magnetic paths of such synchronous motors are very sensitive. The magnets can corrode, for example, if they come in contact with liquids. In addition, they are susceptible to mechanical damage. This is a problem primarily in machine tools, where ferromagnetic particles accrue in large quantities, are attracted by the magnets and can block the air gap between the primary part and the secondary part of the motor.
Thus, for example, U.S. Pat. No. 5,952,742 describes covering the magnetic path of a linear motor with a metallic strip. In addition, the magnets are surrounded by a lateral frame, so that they are protected from all sides.
U.S. Pat. No. 6,882,065 describes cover strips, which are disposed on both sides of the magnetic path of a linear motor. They protect the magnets laterally against harmful influences. On their upper side, these cover strips have a bar whose height corresponds to the thickness of a cover plate. The bars of two opposite cover strips thus form a channel which accommodates and guides the cover plate for covering the magnets. The plate is thus relatively easy to mount. A ferromagnetic plate is held in place by the attractive force of the magnets and does not have to be further secured.
Japanese Published Patent Application No. 2009-38869 describes spacers disposed between the magnets of a magnetic path. These spacers prevent direct contact of the magnets to one another. They also support a cover plate which, due to the spacers, is not in direct contact with the magnets. Forces on the cover plate thus do not affect the magnets.